This invention pertains to chemical-mechanical polishing compositions containing silver salts and their use to polish nickel-containing substrates.
Compositions and methods for planarizing or polishing the surface of a substrate are well known in the art. Polishing compositions (also known as polishing slurries) typically contain an abrasive material in an aqueous solution and are applied to a surface by contacting the surface with a polishing pad saturated with the polishing composition. Typical abrasive materials include silicon dioxide, cerium oxide, aluminum oxide, zirconium oxide, and tin oxide. U.S. Pat. No. 5,527,423, for example, describes a method for chemically-mechanically polishing a metal layer by contacting the surface with a polishing slurry comprising high purity fine metal oxide particles in an aqueous medium. The polishing slurry is typically used in conjunction with a polishing pad (e.g., polishing cloth or disk). Suitable polishing pads are described in U.S. Pat. Nos. 6,062,968, 6,117,000, and 6,126,532, which disclose the use of sintered polyurethane polishing pads having an open-celled porous network, and U.S. Pat. No. 5,489,233, which discloses the use of solid polishing pads having a surface texture or pattern. Alternatively, the abrasive material may be incorporated into the polishing pad. U.S. Pat. No. 5,958,794 discloses a fixed abrasive polishing pad.
Conventional polishing systems and polishing methods typically are not entirely satisfactory at planarizing substrates, especially memory disks. In particular, such polishing systems and polishing methods can result in less than desirable polishing rates and high surface defectivity when applied to memory or rigid disks. Because the performance of many substrates, such as memory disks, is directly associated with the planarity of its surface, it is crucial to use a polishing system and method that results in a high polishing efficiency, selectivity, uniformity, and removal rate and leaves a high quality polish with minimal surface defects.
There have been many attempts to improve the removal rate of memory or rigid disks during polishing, while minimizing defectivity of the polished surface during polishing. For example, U.S. Pat. No. 4,769,046 discloses a method for polishing a nickel-plated layer on a rigid disk using a composition comprising alumina abrasive and a polishing accelerator such as nickel nitrate, aluminum nitrate, or mixtures thereof. U.S. Pat. No. 6,015,506 discloses a method for polishing rigid disks using a polishing composition comprising a dispersion of a metal oxide abrasive, an oxidizing agent, and a catalyst having multiple oxidation states. WO 02/20214 discloses a method for polishing memory or rigid disk substrates using a polishing composition comprising an oxidized halide and an amino acid.
The use of oxidizing silver salts to increase the polishing removal rate of a substrate layer is commonly known in the art. For example, U.S. Pat. No. 5,225,034 discloses a method of polishing copper-containing substrates using a polishing composition comprising water, abrasive, an oxidizing component selected from the group consisting of nitric acid, sulfuric acid, and silver nitrate, or mixtures thereof, and optionally a second oxidant (e.g., H2O2, HOCl, KOCl, KMnO4, CH3COOH). The ""034 patent discloses that the amount of the oxidizing component is about 2% to 15% based on the volume of the polishing composition. U.S. Pat. No. 6,190,237 discloses a polishing composition optionally comprising a chemical etchant (e.g., ferric nitrate, potassium iodate, ammonium cerium nitrate, potassium ferricyanide, hydrogen peroxide, and silver nitrate). U.S. Published Application 2002/0017063 A1 discloses a polishing composition for polishing noble metal substrate comprising water, polycrystalline diamond powder, and at least one additive selected from the group consisting of oxidizing agents (e.g., AgNO3, Na2S2O8, and combinations thereof), complex-forming agents, surfactants, and organic bases. U.S. Published Application 2002/0004360 A1 discloses a polishing composition comprising inorganic compounds (e.g., Ag compounds) or organic compounds as abrasive grains.
A need remains, however, for polishing systems and polishing methods that will exhibit desirable planarization efficiency, selectivity, uniformity, and removal rate during the polishing and planarization of substrates, especially memory disks, while minimizing defectivity, such as surface imperfections and damage to underlying structures and topography during polishing and planarization.
The invention seeks to provide such a chemical-mechanical polishing system and method. These and other advantages of the invention will be apparent from the description of the invention provided herein.
The invention provides a method of polishing a nickel-containing substrate comprising (i) contacting the substrate with a chemical-mechanical polishing system comprising an abrasive, a polishing pad, or both an abrasive and a polishing pad, a silver salt comprising a silver ion, and a liquid carrier, and (ii) abrading at least a portion of the substrate to polish the substrate. The invention further provides a chemical-mechanical polishing system comprising (a) an abrasive, a polishing pad, or both an abrasive and a polishing pad, (b) a liquid carrier, (c) a silver salt comprising a silver ion, and (d) a secondary oxidizing agent, wherein the amount of the silver ion is about 0.1 wt. % to about 3 wt. % and the wt. % amount of the secondary oxidizing agent is about 3 times or less than the wt. % amount of the silver ion, based on the weight of the liquid carrier and anything dissolved or suspended therein.